There are a number of ways to implement refractive index sensing, which include using a fiber Bragg grating (FBG), long period grating (LPG), macro-bend single-mode fiber (SMF), surface plasmon resonance (SPR), a Fabry-Perot interferometer (FPI), a multi-D-shaped optical fiber or a single-mode-multimode-single-mode (SMS) fiber structure. For these sensors, the RI information is extracted by measuring the RI-induced shift in the peak wavelength of these sensors' spectrum, which involves a complex and expensive system.